Within the field of machining and more specifically precision boring of holes there is a need for a reliable, rigid, simple, and micro adjustable boring bar. There are numerous examples of attempts to provide precision adjustment but most are complex and inherently weaken the fundamental rigidity of the tool to accommodate their means of adjustment, such as gears and complex bearings. There are also examples of units that provide an adjustable bore size but lack the fine adjustment required to compensate for tool wear. This fine adjustment capability is increasingly important in today's ultra precise machining requirements.